NEET-PG 2015 - Microbiology PYQs Practice Questions

Q: Bacteria most commonly involved in bowel decomposition after death is?

Clostridium perfringens. ***Clostridium perfringens*** - This bacterium is a ubiquitous **anaerobe** in the gut and is known for its rapid proliferation after death, producing gases that contribute to **bloating and decomposition**. - It is a primary cause of **gas gangrene** in living individuals, reflecting its tissue-destructive capabilities, which extend to post-mortem changes. - Produces large amounts of **hydrogen and CO2**, making it the most significant contributor to post-mortem gas formation and putrefaction. *Streptococcus pyogenes* - While a significant pathogen in life, causing conditions like **strep throat** and **necrotizing fasciitis**, it is not the primary agent of putrefaction. - Its role in post-mortem decomposition is generally less prominent compared to anaerobic gut flora. *Pseudomonas aeruginosa* - This bacterium is an opportunistic pathogen often associated with infections in immunocompromised individuals or in healthcare settings. - It is not typically identified as the most common or primary bacterium involved in the initial stages of post-mortem **bowel decomposition**, though it can be present in later stages. *Escherichia coli* - While *E. coli* is abundant in the bowel and participates in post-mortem decomposition, it is not the **most common** agent responsible for gas production and tissue decomposition. - *Clostridium perfringens* proliferates more rapidly and produces significantly more gas, making it the predominant bacterium in bowel putrefaction. [Practice more Microbiology PYQs on OnCourse]

Q: Interleukin 2 is produced by

T helper cells 1. ***T helper cells 1*** - **T helper 1 (Th1) cells** are a primary source of **interleukin-2 (IL-2)**, which is crucial for the proliferation and survival of T cells. - IL-2 acts as a **T-cell growth factor**, promoting the expansion of activated T cells, including cytotoxic T lymphocytes. *T helper cells 2* - **T helper 2 (Th2) cells** primarily produce cytokines like **IL-4, IL-5, IL-6, IL-10, and IL-13**, which are involved in humoral immunity and allergic responses. - While Th2 cells are important for immune responses, they are not major producers of IL-2. *Natural killer cells* - **Natural killer (NK) cells** are part of the innate immune system and produce cytokines such as **interferon-gamma (IFN-$\gamma$)** and **tumor necrosis factor-alpha (TNF-$\alpha$)**. - They are not a significant source of IL-2, which is primarily a T-cell derived growth factor. *Basophils* - **Basophils** are granulocytes involved in allergic reactions and anti-parasitic immunity, producing mediators like **histamine** and cytokines such as **IL-4** and **IL-13**. - Basophils do not produce IL-2; their role is distinct in the immune response compared to T cells. [Practice more Microbiology PYQs on OnCourse]

Q: IFN-gamma is produced by

T-cells. ***T-cells*** - **Interferon-gamma (IFN-γ)** is a crucial cytokine primarily produced by **activated T-lymphocytes**, especially **Th1 cells** and **cytotoxic T lymphocytes (CTLs)**. - Natural killer (NK) cells also produce **IFN-γ**, which plays a key role in **antiviral** and **antitumor immunity**, as well as in promoting **Type 1 immune responses**. *Macrophages* - While macrophages are **responsive to IFN-γ** (e.g., becoming activated), they are not the primary producers of this cytokine. - Macrophages primarily produce other cytokines such as **IL-1, IL-6, TNF-alpha**, and **IL-12** in response to infection or inflammation. *Neutrophils* - **Neutrophils** are key phagocytes in the innate immune system and are primarily involved in engulfing and killing pathogens. - They are not known to be a significant source of **IFN-γ** production; their main defensive mechanisms involve **phagocytosis**, **degranulation**, and **NETosis**. *B-cells* - **B-cells** are central to humoral immunity, specializing in **antibody production** and acting as **antigen-presenting cells**. - They generally do not produce **IFN-γ**; instead, their cytokine repertoire includes **IL-10**, **IL-6**, and **lymphotoxin**. [Practice more Microbiology PYQs on OnCourse]

Q: The process by which antigen-specific B lymphocytes are selected and activated to proliferate and produce antibodies is called:

Clonal selection. ***Clonal selection*** - **Clonal selection** is the fundamental process by which an antigen-specific B lymphocyte is **selected** when its B cell receptor (BCR) recognizes and binds to a matching antigen. - This binding triggers the B cell to become **activated**, **proliferate** (undergo clonal expansion), and **differentiate** into plasma cells that produce antibodies specific to that antigen. - This process is the cornerstone of **adaptive immunity**, ensuring that only B cells with receptors matching the encountered antigen are stimulated to respond. *Class switching* - **Class switching** (isotype switching) occurs AFTER clonal selection and activation. - It allows already-activated B cells to change the **antibody class** they produce (from IgM to IgG, IgA, or IgE) while maintaining the **same antigen specificity**. - This process modifies effector functions but does NOT involve the initial selection and activation of antigen-specific B cells. *Group switching* - This is not a recognized term in immunology. - It does not describe any standard process of B cell activation or antibody production. *Hybridisation* - **Hybridization** refers to the formation of double-stranded nucleic acids from complementary strands or the creation of hybrid cells (e.g., hybridomas for monoclonal antibody production). - It is not the physiological process by which B lymphocytes are selected and activated in response to antigen exposure. [Practice more Microbiology PYQs on OnCourse]

Q: In the context of immune response, which of the following cell types does not express MHC class II molecules?

NK cells. ***NK cells*** - **Natural Killer (NK) cells)** are innate lymphocytes that do **NOT express MHC class II molecules** under any circumstances. - NK cells use alternative recognition mechanisms (KIRs, activating receptors) to detect target cells, primarily recognizing the **absence of MHC class I** or stress-induced ligands. - They function in innate immunity without antigen presentation capability. - **This is the best answer** as NK cells never express MHC class II, making them distinctly different from professional APCs. *Cortical macrophages* - **Cortical macrophages** in lymphoid organs are professional **antigen-presenting cells (APCs)** that constitutively express **MHC class II molecules**. - They present processed antigens to CD4+ T helper cells, playing a crucial role in initiating adaptive immune responses. *Medullary macrophages* - **Medullary macrophages** are also professional APCs that constitutively express **MHC class II molecules**. - They participate in antigen presentation and immune surveillance within the medullary regions of lymphoid tissues. *Neutrophils* - Neutrophils are granulocytes that **typically do not constitutively express MHC class II molecules** in their resting state. - However, under certain inflammatory conditions with prolonged stimulation (IFN-γ, GM-CSF), neutrophils can be induced to express low levels of MHC class II. - While neutrophils generally lack MHC class II, **NK cells are the more definitive answer** as they never express MHC class II under any physiological or pathological conditions. [Practice more Microbiology PYQs on OnCourse]

Question 1

Bacteria most commonly involved in bowel decomposition after death is?

Accepted Answer

Clostridium perfringens

Answer

Streptococcus pyogenes

Answer

Pseudomonas aeruginosa

Answer

Escherichia coli

Question 2

Interleukin 2 is produced by

Accepted Answer

T helper cells 1

Answer

T helper cells 2

Answer

Natural killer cells

Answer

Basophils

Question 3

IFN-gamma is produced by

Accepted Answer

T-cells

Answer

Macrophages

Answer

Neutrophils

Answer

B-cells

Question 4

The process by which antigen-specific B lymphocytes are selected and activated to proliferate and produce antibodies is called:

Accepted Answer

Clonal selection

Answer

Class switching

Answer

Group switching

Answer

Hybridisation

Question 5

In the context of immune response, which of the following cell types does not express MHC class II molecules?

Accepted Answer

NK cells

Answer

Cortical macrophages

Answer

Neutrophils

Answer

Medullary macrophages

Question 6

"Citron bodies" are boat- or leaf-shaped pleomorphic organisms found in exudates. This is a characteristic feature of which organism?

Accepted Answer

Cl. septicum

Answer

Cl. edematiens

Answer

Cl. tetani

Answer

Cl. welchii

Question 7

Which bacteria can be isolated using crystal violet blood agar?

Accepted Answer

β-hemolytic streptococci

Answer

Corynebacterium diphtheriae

Answer

Staph aureus

Answer

Meningococcus

Question 8

Viral DNA is integrated into Bacterial DNA in:

Accepted Answer

Lysogenic cycle

Answer

Bacterial transduction

Answer

Bacterial transformation

Answer

Bacterial conjugation

Question 9

Multiple drug resistance is transferred through -

Accepted Answer

Conjugation

Answer

Transduction

Answer

Transformation

Answer

Mutation

Question 10

Which medium is most commonly used for antibiotic sensitivity testing?

Accepted Answer

Mueller-Hinton agar

Answer

CLED agar

Answer

Blood agar

Answer

MacConkey agar

NEET-PG 2015 — Microbiology